Zero insertion force electrical connector and terminal

ABSTRACT

A zero insertion force electrical connector for use with a device having an array of pin terminals including a lower connector housing having a top surface and a plurality of cavities in the top surface corresponding to the array of pin terminals. Each of the cavities includes a base wall spaced from the top surface. A plurality of resilient terminals are mounted in the cavities. Each of the terminals includes a mounting portion for securing the terminal in the base wall, a free end portion, a contact structure adjacent the free end portion and a spring arm portion between the base wall and the contact structure. The pin terminals are moved in the cavities in a first direction along a path of travel between an unmated position wherein the pins are spaced from the contact structures in the cavities and a mated position wherein the pins are fully mated with the contact structures. The contact structure includes a pin engagement surface at least partly inclined with respect to the path of travel. The spring arm portion of each of the terminals is a generally flat and planar leaf region oriented generally parallel to the first direction. The leaf region includes a first side edge at a side of the terminal where the pin first engages the contact structure and a second side edge extending from the mounting portion to the contact structure at the opposite side of the terminal. Notch means is provided in at least one of the side edges for increasing the flexibility of the leaf portion.

FIELD OF THE INVENTION

The present invention relates to electrical connectors and moreparticularly to an improved zero insertion force electrical connectorfor high frequency pin grid array devices.

BACKGROUND OF THE INVENTION

A pin grid array (PGA) device such as a microprocessor may have many pinterminals, numbering in the hundreds. Electrical connectors are used tomount PGA devices on a printed circuit board and establish electricalconnections between the pin terminals of the PGA device and conductorsof the printed circuit board. A typical electrical connector permits thePGA device to be removed for repair or upgrade purposes. Anotherbeneficial result is that the PGA device is not subjected to heat whenthe connector is soldered to a printed circuit board.

In some known electrical contact systems, when a pin terminal isinserted into a cavity of the connector, it contacts and resilientlydeforms a mating terminal. As a result forces are required to mate andunmate such a contact system. Mating forces are not desirable inelectrical connectors for devices such as PGA devices because the largenumber of contacts results in large cumulative forces that could damagesome of the pins of the PGA device. When there is a need to eliminatemating forces, a connector known as a zero insertion force (ZIF)connector can be used.

A typical zero insertion force connector for PGA devices includes alower housing with numerous cavities corresponding to the array of pinterminals of a PGA device. A resilient electrical terminal is mounted ineach cavity. An upper housing includes numerous openings through whichthe pin terminals of the PGA device extend. The upper housing can bemoved relative to the lower housing between a first free or unmatedposition and a second locked or fully mated position. In the freeposition, the PGA device can be placed with no contact insertion forceupon the upper housing with the pin terminals extending through theupper housing and into regions in the cavities of the lower housingwhere they are spaced from the resilient terminals. The upper housing isthen moved relative to the lower housing, causing the pin terminals tomove into contact with the resilient terminals in the cavities.

U.S. Pat. Nos. 4,498,725 to Bright et al. and 4,750,891 to Egawa atFIGS. 5 and 7 disclose zero insertion force connectors with resilientterminals having contact structures in the form of a pair of spacedapart resilient opposed fingers between which a pin terminal may bereceived.

U.S. Pat. Nos. 3,315,212 to Peterson, 4,674,811 to Corwin, 4,750,891 toEgawa at FIGS. 8A and 8B and 4,887,974 to Ichimura et al. disclose zeroinsertion force connectors with terminals having free ends with contactstructures and spring portions that flex in the same direction as thepin terminals move in order to provide a contact force.

U.S. Pat. No. 4,988,310 to Bright et al. discloses a zero insertionforce connector having terminals with an upstanding beam, a cantileverbeam portion extending laterally from the upstanding beam and a contactarea upon the cantilever beam acting to cause torsional deflection ofthe cantilever beam in the mated condition.

U.S. Pat. No. 5,342,214 to Hsu discloses a zero insertion forceconnector having two upstanding terminal portions, one including alaterally extending guide portion 430 and a noninclined contact portion43.

Pending U.S. patent application Ser. No. 08/367,566 filed on Jan. 3,1995 discloses and claims a zero insertion force connector with flexibleterminals each having a mounting portion, a leaf spring portion and acontact structure at a free end. The leaf spring portion flexes in adirection perpendicular to the direction of movement of the pin terminalrelative to the flexible terminal, and the contact structure includes aninclined ramp surface generally disposed within the lateral bounds ofthe leaf spring portion.

The zero insertion force connector of said U.S. patent application Ser.No. 08/367,566 has advantages including small contact pitch or spacing,a simple sturdy shape and minimum contact plating requirements. However,in some applications it is desirable to reduce the inductance when usedwith PGA devices operating at very high speeds or frequencies.

Shortening the length of the terminal would reduce the inductance butcould lead to other problems such as large contact mating forces oroverstressing of the terminal beams. In addition, the terminals of thatconnector are inserted from the top of the connector housing and theterminal mounting force may need to be applied to the free end of theterminal and not directly to the mounting portion.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide an improved zeroinsertion force connector and terminal having low impedance and suitedfor use in high frequency applications. Another object is to provide azero insertion force connector with a terminal having a small lengthbetween a mounting portion and a free end and having low contact matingforce, low mechanical stress and substantial normal contact force whenfully mated. Other objects are to provide a terminal for zero insertionforce connectors that is loaded from the bottom of a housing with aloading force applied directly to the terminal mounting portion, and toprovide a terminal having structure for preventing the wicking of solderthrough an enlarged mounting opening used to facilitate loading theterminal from the bottom of the housing.

In brief, in accordance with the invention, there is provided a zeroinsertion force electrical connector for use with a device having anarray of pin terminals. The electrical connector includes a lowerconnector housing having a top surface and a plurality of cavities inthe top surface corresponding to the array of pin terminals. Each of thecavities includes a base wall spaced from the top surface. A pluralityof resilient terminals are mounted in the cavities.

Each of the terminals includes a mounting portion for securing theterminal in the base wall, a free end portion, a contact structureadjacent the free end portion and a spring arm portion between the basewall and the contact structure. The pin terminals are moved in thecavities in a first direction along a path of travel between an unmatedposition wherein the pins are spaced from the contact structures in thecavities and a mated position wherein the pins are fully mated with thecontact structures. The contact structure includes a pin engagementsurface at least partly inclined with respect to the path of travel. Thespring arm portion of each of the terminals is a generally flat andplanar leaf region oriented generally parallel to the first direction.The leaf region includes a first side edge at a side of the terminalwhere the pin first engages the contact structure and a second side edgeextending from the mounting portion to the contact structure at theopposite side of the terminal. Notch means is provided in at least oneof the side edges for increasing the flexibility of the leaf portion.

In brief, in accordance with another feature of the invention, there isprovided a zero insertion force electrical connector including aconnector housing having a top surface and a plurality of cavities inthe top surface corresponding to an array of pin terminals. Each of thecavities includes a base wall spaced from the top surface and terminalretention openings in the base wall. A plurality of terminals aremounted in the cavities. Each of the terminals is a stamped and formedsegment of flat and planar metal stock including a mounting portionsubstantially in the plane of the stock, a free end portion, a contactstructure adjacent the free end portion and a spring arm portion betweenthe mounting portion and the contact structure. The pin terminals aremoved in the cavities between an unmated position wherein the pins arespaced from the contact structures in the cavities and a mated positionwherein the pins are mated with the contact structures. The terminalmounting portion of each terminal is received in one of the terminalretention openings for securing the terminal in the cavity. The contactstructure includes a pin engagement surface raised from the plane of thestock. The terminal retention opening has an enlarged portion permittingentry of the contact structure into the cavity through the base wall.The mounting portion has a projection extending out of the plane of thestock and substantially blocking the enlarged portion when the mountingportion is received in the terminal retention opening.

BRIEF DESCRIPTION OF THE DRAWING

The present invention together with the above and other objects andadvantages may best be understood from the following detaileddescription of the preferred embodiment of the invention illustrated inthe drawings, wherein:

FIG. 1 is an isometric view of a PGA device mounted on an electricalconnector constructed in accordance with the present invention;

FIG. 2 is an isometric view on an enlarged scale of a resilientelectrical terminal of the connector of FIG. 1;

FIG. 3 is a fragmentary top plan view on an enlarged scale of part ofthe top surface of the lower housing of the connector of FIG. 1 with apin terminal of the PGA device shown in section in the initial free orunmated position and shown with a broken line in the fully matedposition;

FIG. 4 is a fragmentary bottom plan view of part of the bottom surfaceof the lower housing illustrating a terminal and a terminal retentionopening;

FIG. 5 is a fragmentary sectional view of the electrical connector takenalong the line 5--5 of FIG. 3; and

FIG. 6 is a fragmentary sectional view of the rear of the terminalwithin the electrical connector taken along the line 6--6 of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Having reference now to the drawings, FIG. 1 illustrates a zeroinsertion force connector designated as a whole as 20 used with a PGAdevice 22. In a preferred arrangement the PGA device may be amicroprocessor having hundreds of pin terminals 24 (FIG. 3) typically ina staggered array. Connector 20 is mounted by soldering to a printedcircuit board (not shown) and releasably receives the device 22 in orderto make electrical connections between the pin terminals 24 andconductive areas of the printed circuit board.

In general, the zero insertion force connector 20 includes a lowerhousing 26 and an upper housing 28. Latch and guide structures 30 areprovided on the housings 26 and 28 in order to removably secure theupper housing 28 on an upper surface 32 (FIGS. 3, 5 and 6) of the lowerhousing 26. The housings 26 and 28 are relatively movable in the planeof the surface 32 in the direction indicated by an arrow 34 in FIGS. 1and 3. An operating lever 36 is rotatably supported by the lower housing26 and engages the upper housing 28 to move it between a first free orunmated position and a second locked or fully mated position. In theserespects, the housings 26 and 28 and the lever 36 may be conventional,and reference may be had to U.S. Pat. No. 4,498,725, incorporated hereinby reference, for a disclosure of one conventional arrangement.

Upper housing 28 includes an upper surface 38 upon which the device 22is mounted and a lower surface that slides across the upper surface 32of lower housing 26 in response to manipulation of the operating lever36. Numerous openings (not shown) extend through the upper housing 28from the upper surface 38 and the openings are arrayed in the samepattern as the array of pin terminals 24 so that the device 22 can beplaced upon the surface 38 with male pin terminals 24 extending throughthe openings of the upper housing 28. A further disclosure of onesuitable form of upper housing 28 is found in pending U.S. patentapplication Ser. No. 08/367,566 filed on Jan. 3, 1995, incorporatedherein by reference.

The lower housing 26 has a lower surface 40 generally parallel to theupper surface 32. A plurality of cavities 42 extend from the uppersurface 32 toward the lower surface 46. Cavities 42 correspond to thearray of pin terminals 24 such that an individual cavity may be providedfor each pin terminal 24 or a single cavity may receive more than onepin terminal 24. A portion of one cavity 42 is seen in FIGS. 3, 5 and 6.

The cavity 42 extends down to a base wall 44 having an upper surface 46spaced from the lower surface 40. A generally T-shaped terminal mountingopening 48 extends through the base wall 44 between the upper and lowersurfaces 46 and 40. The cavity 42 is also defined by an upstanding sidewall 50 defining a pin terminal receiving region 52 and a terminalcontact region 54 (FIG. 3). Side wall 50 includes a pin terminal guideramp 56 and a pin terminal backing wall 58 (FIG. 3).

Numerous resilient terminals 60 are mounted in the lower housing 26 forcontacting the pin terminals 24 of the PGA device 22. Each resilientterminal 60 includes a mounting portion 62 received in the terminalmounting opening 48 of the base wall 44. Extending downward from themounting portion 22 is a solder tail portion 64 for connection to aplated through hole of the printed circuit board (not shown) upon whichthe connector 20 is mounted. Alternatively, a surface mount tail orother tail configuration could be used. Extending upward from themounting portion 22 is a flexible and resilient spring arm portion 66 inthe form of a flat and planar leaf region. A contact structure 68 islocated above the spring arm portion 66 near a free end 70 of theterminal 60. The terminals 60 are small enough to permit terminalsformed in a stamping and forming operation from a single sheet of flatplanar sheet metal stock to be inserted at close spacings before theterminals are severed from a single carrier strip.

In the free or unmated position of the housings 26 and 28, the pinterminals 24 are initially received without a mating or insertion forcein the pin terminal receiving regions 52 of the cavities 42. Theinitial, unmated pin terminal position is seen in solid lines in FIG. 3.When the lever 36 is used to move the housings to the fully matedposition, each pin terminal 24 moves in the direction of the arrow 34 inFIG. 3 relative to the lower housing 26 into the terminal contact region54 of the cavity 48. The fully mated position of the pin terminal incavity 42 is seen as 24A in broken lines in FIG. 3. The guide ramp 56and backing wall 58 guide the pin terminal 24 into the fully matedposition.

The contact structure 68 is formed to project above or out of the planeof the metal stock from which the terminal 60 is made. As the pinterminal 24 moves relative to the resilient terminal 60 in the directionof the arrow 34 in FIG. 3, it engages a raised pin engagement surface 71of the contact structure 68 and the spring arm portion 66 resilientlyflexes to apply a contact mating force to the contact interface as thecontact structure 68 moves away from the wall 58 in a directionperpendicular to the direction of the arrow 34. The contact structure 68is preferably as described in pending U.S. patent application Ser. No.08/367,566 filed on Jan. 3, 1995, and reference may be had to thatapplication for a further description of the structure, operation andadvantages of the contact structure 68.

Because PGA devices such as microprocessors operate at increasinglyhigher frequencies, it is important to reduce the impedance ofassociated electrical connectors. The physical size of the resilientterminal 60 affects the high speed electrical performance. Increasedlength of the spring portion 66 increases inductance. Decreases in crosssectional area of spring portion 66 can also degrade high frequencyelectrical performance. It is desirable to decrease the spring length toreduce inductance while minimizing reduction of cross sectional area,and to maintain a desired predetermined normal resilient contact forceof the mated contacts without a substantial increase in the cam forcesincurred as the mating contacts engage and move relative to one another.

The spring arm portion 66 includes a pair of arc-shaped notches orindentations 72 and 74 in opposed side edges 76 and 78 of the springportion 66 as best seen in FIGS. 2 and 6. The center of the radius ofeach arc is located outside the side edges 76, 78 of the terminals 60.The side edge 76 is located at the side of the terminal 60 where the pinengagement surface 71 is initially contacted by the pin terminal 24, andthe opposite side edge 78 is adjacent the fully mated contact interfacelocation. Notches 72 and 74 are not vertically aligned with one anotherbut rather are offset from one another along the length of the springportion 66. The notch 74 is relatively closer to the contact structure68 and the notch 72 is relatively closer to the mounting portion 62.

This notch configuration has important advantages. The spring portion 66is made relatively short, thereby minimizing inductance. The notches 72and 74 increase the flexibility of the spring portion 66 so thatexcessive normal mating forces are avoided even though the spring lengthis decreased. Because the notches 72 and 74 are not aligned, they do notresult in a narrow neck region that would have electrical and mechanicaldisadvantages including increased impedance, concentration of mechanicalstress and susceptibility to plastic deformation. Furthermore, thenotches are preferably arc-shaped in order to reduce stressconcentrations in the beam.

The offset notches 72 and 74 impart a somewhat diagonal or slightly Sshaped configuration to the spring portion 66. This has the beneficialeffect of making the spring portion 66 act as a relatively short memberelectrically but as a relatively longer beam member mechanically. Springportion 66 serves primarily as a cantilever leaf spring, flexing in thedirection perpendicular to the contact mating direction of arrow 34.However, the notch 74 adjacent to the contact structure 68 andunderlying the region where the pin terminal 24 first contacts thecontact structure permits a limited and transitory torsional deflection,increasing flexibility as contact is initiated near the side edge 76.The contact structure is permitted to rotate slightly as contact ismade. Then as the fully mated position is approached closer to the sideedge 78 of the contact region, the contact structure rotates back. Inthe fully mated position, substantially pure cantilever flexing occurswith no significant torsional deflection.

A further advantage of the connector 20 is that the resilient terminals60 are loaded into the lower housing 26 from beneath the base wall 44.In connectors of the same type where the terminals are loaded fromabove, the terminal insertion tooling may apply some of the terminalmounting force to the free end of the terminal because there is notsufficient room within the terminal receiving cavity for the tooling.Forces applied to the free end of the terminal can damage the contactstructure or the spring arm portion.

The mounting portion 62 of the terminal 60 is generally a flat, planarelement in the plane of the stock of the metal from which the terminal60 is made. A pair of positioning feet 80 are formed on the portion 62for increasing the force with which the terminal is retained and foraccurately locating the terminal in the cavity 42. Mounting portion 62is pressed with a frictional, interference fit into a correspondinglyshaped portion of the terminal mounting opening 48. Once positionedwithin terminal mounting opening 48, the lateral edges of the mountingportion 62 engage end walls of the opening 48 and feet 80 and thesurface of mounting portion 62 opposite feet 80 engage the sidewalls ofmounting portion 62 in order to securely hold the terminals on allsides.

The mounting portion 62 of the terminal 60 has downwardly facingshoulders 82 that can be directly engaged by tooling for forcing themounting portion 62 upward into the terminal mounting opening 48. Slopedentry surfaces 84 are formed on the upper corners of the mating portion62 to guide and facilitate movement of the portion 62 into the opening48.

Because the resilient terminal 60 is installed from below, the contactstructure 68 must pass through the terminal mounting opening 48. Contactstructure 68 projects above or out of the plane of the sheet metal stockfrom which the terminal 60 is made. To provide clearance, the terminalreceiving opening 48 has an enlarged portion 86 seen in FIGS. 3-5.

As such, it can be seen in FIG. 4 that the terminal receiving cavity 48is generally T-shaped. The base or stem of the T-shape is slightlylonger than the distance the contact structure 68 projects out of orabove the plane of the sheet metal stock from which it is formed inorder to permit the contact structure to pass through the cavity 48. Asstated above, the cross member of the T-shape receives mounting portion62 of the terminal in an interference fit. As a result, the cross memberof the T-shape is slightly smaller than the mounting portion 62.

When the pin contact portion 64 of the terminal 60 is soldered to aprinted circuit board, molten solder can flow or wick upward along themetal surfaces of the terminal. The enlarged portion 86 of the terminalreceiving opening 48 could provide a path for the flow of solder throughthe base wall 44 and into the cavity 42. To prevent such solder wicking,a projection 88 is formed on the mounting portion 62 of the terminal 60.As best seen in FIGS. 4 and 5, the projection 88 is approximately atleast as large as the contact structure 68 and substantially blocks orfills the enlarged portion 86 leaving only clearances too small for theflow of solder. The projection 88 is formed as a tab struck from themounting portion 62, but other configurations of projection could beused. By striking the projection 88 from mounting portion 62, a hole iscreated in mounting portion 62. As the terminals are soldered to aprinted circuit board, if solder attempts to wick up the terminal, thesolder will attempt to fill the opening 89 created when projection 88was formed rather than continuing up the terminal 60 into the contactstructure 68.

While the present invention has been described with reference to thedetails of the embodiment of the invention shown in the drawing, thesedetails are not intended to limit the scope of the invention as claimedin the appended claims.

We claim:
 1. A zero insertion force electrical connector for use with adevice having an array of pin terminals, said electrical connectorcomprising:a dielectric housing having a lower component and an uppercomponent slidably mounted thereon, said lower component having a topsurface and a plurality of cavities in said top surface corresponding tothe array of pin terminals; each of said cavities including a base wallspaced from said top surface; a plurality of resilient terminals mountedin said cavities, each said terminal including a mounting portion forsecuring said terminal in said base wall, a free end portion, a contactstructure adjacent said free end portion and a spring arm portionextending from said base wall to said contact structure; and means formoving the pin terminals in said cavities in a first direction along apath of travel between an unmated position wherein the pins are spacedfrom said contact structures in said cavities and a mated positionwherein the pins are fully mated with said contact structures; saidcontact structure including a pin engagement surface at least partlyinclined with respect to said path of travel; said spring arm portion ofeach said terminal being a generally flat and planar region orientedgenerally parallel to said first direction; said generally flat andplanar region including a first side edge extending from said mountingportion to said contact structure at a side of said resilient terminalwhere one of the pin terminals first engages said contact structure anda second side edge extending from said mounting portion to said contactstructure at the opposite side of said terminal, said first and secondside edges being generally parallel; and notch means in at least one ofsaid side edges for increasing the flexibility of said spring armportion, said notch means including a generally arc-shaped notch.
 2. Azero insertion force electrical connector as claimed in claim 1, saidnotch being located in said first side edge.
 3. A zero insertion forceelectrical connector as claimed in claim 2, said notch being located insaid side edge closer to said contact structure than to said mountingportion.
 4. A zero insertion force electrical connector as claimed inclaim 2, further including a second notch in said second side edge.
 5. Azero insertion force electrical connector as claimed in claim 4, saidfirst and second notches being offset along the length of said generallyflat and planar region.
 6. A zero insertion force electrical connectoras claimed in claim 5, said first notch being closer to said contactstructure than said second notch.
 7. A zero insertion force electricalconnector as claimed in claim 6, wherein said second notch isarc-shaped.
 8. A zero insertion force electrical connector as claimed inclaim 1, wherein said arc-shaped notch has a center of radius outsidesaid side edges of the terminal.
 9. A zero insertion force electricalconnector as claimed in claim 6, wherein said arc-shaped notches eachhave a center of radius outside said side edges of the terminal.
 10. Azero insertion force electrical connector as claimed in claim 1 whereinsaid terminal is a stamped and formed segment of flat and planar metalstock;said pin engagement surface being raised above the plane of saidmetal stock; said mounting portion lying substantially in the plane ofsaid metal stock and said base wall including a terminal retentionopening receiving said mounting portion; said retention opening havingan enlarged portion permitting said pin engagement surface to passthrough said base wall; and said mounting portion having a projectionextending out of the plane of said metal stock substantially blockingsaid enlarged portion.
 11. A zero insertion force electrical connectoras claimed in claim 1 wherein said first and second side edges aresubstantially parallel.
 12. A zero insertion force electrical connectoras claimed in claim 1 wherein said spring arm portion has a widthbetween said first and second side edges and said contact structure hasa width generally the same as said spring arm width.
 13. A terminalcomprising:a tail portion for interconnecting to an electroniccomponent; a mounting portion for securing said terminal in a housing; afree end portion; a contact structure adjacent said free end portion;and a generally flat and planar spring arm portion extending from saidmounting portion to said contact structure; said contact structureincluding an engagement surface at least partly inclined relative tosaid spring arm portion for engaging a contact of a mating electronicdevice; said generally flat and planar spring arm including first andsecond generally parallel side edges extending from said mountingportion to said contact structure; and an arc-shaped notch in each ofsaid side edges for increasing the flexibility of said spring arm, saidnotches being offset relative to each other along the length of saidspring arm.
 14. A terminal as claimed in claim 13, wherein said notch insaid second side edge is located closer to said contact structure thanto said mounting portion.
 15. A terminal as claimed in claim 13, whereinsaid arc-shaped notches each have a center of radius outside said sideedges of the terminal.
 16. A terminal as claimed in claim 13 whereinsaid spring arm portion has a width between said first and second sideedges and said contact structure has a width generally the same as saidspring arm width.
 17. A zero insertion force electrical connector foruse with a device having an array of pin terminals, said electricalconnector comprising:a dielectric housing having a lower component andan upper component slidably mounted thereon, said lower component havinga top surface and a plurality of cavities in said top surfacecorresponding to the array of pin terminals; each of said cavitiesincluding a base wall spaced from said top surface; a plurality ofresilient terminals mounted in said cavities, each said terminalincluding a mounting portion for securing said terminal in said basewall, a free end portion, a contact structure adjacent said free endportion and a spring arm portion extending from said base wall to saidcontact structure; and means for moving the pin terminals in saidcavities in a first direction along a path of travel between an unmatedposition wherein the pins are spaced from said contact structures insaid cavities and a mated position wherein the pins are fully mated withsaid contact structures; said contact structure including a pinengagement surface at least partly inclined with respect to said path oftravel; said spring arm portion of each said terminal being a generallyflat and planar region oriented generally parallel to said firstdirection; said generally flat and planar region including asubstantially straight first side edge extending from said mountingportion to said contact structure at a side of said resilient terminalwhere one of the pin terminals first engages said contact structure anda substantially straight second side edge extending from said mountingportion to said contact structure at the opposite side of said terminal;and a notch in each said side edges for increasing the flexibility ofsaid spring arm portion, each of said notches being generally arc-shapedand said notches being offset along the length of said generally flatand planar region.
 18. A zero insertion force electrical connector asclaimed in claim 17, wherein said notch in said second side edge iscloser to said contact structure than said notch in said first sideedge.
 19. A zero insertion force electrical connector as claimed inclaim 17, wherein said arc-shaped notches each have a center of radiusoutside said side edges of the terminal.
 20. A zero insertion forceelectrical connector as claimed in claim 17 wherein said terminal is astamped and formed segment of flat and planar metal stock;said pinengagement surface being raised above the plane of said metal stock;said mounting portion lying substantially in the plane of said metalstock and said base wall including a terminal retention openingreceiving said mounting portion; said retention opening having anenlarged portion permitting said pin engagement surface to pass throughsaid base wall; and said mounting portion having a projection extendingout of the plane of said metal stock substantially blocking saidenlarged portion.
 21. A zero insertion force electrical connector asclaimed in claim 17 wherein said first and second side edges aresubstantially parallel.
 22. A zero insertion force electrical connectoras claimed in claim 17 wherein said spring arm portion has a widthbetween said first and second side edges and said contact structure hasa width generally the same as said spring arm width.